The knee ligaments are short bands of tough fibrous connective tissue that guide normal joint motion and restrict abnormal joint movement. Although the injury and healing of knee ligaments have been topics of extensive study, fundamental information about the relationship between the ultrastructure of the tissue and its continuum level mechanical behavior is severely lacking. The decorin-based proteoglycans play an important role in collagen fibrillogenesis and may be important determinants of the material behavior of connective tissues. The objectives of this research are to investigate the roles of decorin-based proteoglycan crosslinks and fluid flow in the elastic and viscoelastic material behavior ligaments. The hypotheses to be addressed are 1) decorin-based crosslinks control the resistance of ligament to tensile loading transverse to the fiber direction and shear loading along the fiber direction by stretching during relative movement of the collagen fibrils; 2) a transversely isotropic hyperelastic constitutive model that incorporates structural information regarding decorin crosslinks and collagen fiber crimp will describe and predict the elastic material behavior of human knee ligaments; 3) The viscoelastic material behavior of ligament is due to fluid movement. These hypotheses will be addressed through a series of aims that combine experimental measurements from the molecular level to the continuum level. The results of this study will have important implications for understanding the fundamental role of the small proteoglycans and fluid flow in the viscoelastic behavior of fibrous connective tissues, and will help to understand the phenotypes associated with disease states that are related to deficiencies in the small proteoglycans. [unreadable] [unreadable]